Homologies and Analogies

 

Few animals may seem to be as far apart on the spectrum when it comes to similarities as a whale and a bird. Birds fly through the sky with the help of their feather covered wings and flippers make it possible for whales to maneuver through the ocean. But the wings of a bird and flippers on whales are much more similar than you may think. In fact, both tetrapod limbs are a homologous trait that they inherited from their common tetrapod ancestor. This ancestor, the first tetrapod, is believed by scientists to have roamed the Earth 350 million years ago and had limbs with one humerus attached to the radius and ulna.







Unlike the obvious lack of similarities between whales and birds there are some animals that look strikingly similar but are very different such as the Northern Flying Squirrel and the Sugar Glider. These two animals live in separate parts of the world. The Northern Flying Squirrel lives in North America and Sugar Gliders are found in Australia but they share analogous structures. They are both nocturnal and have big eyes to assist them in seeing at night and a thin piece of skin that stretches between their arms and legs to help them glide when leaping from high places. Though these very distant relatives look so much alike the are quite different. The Sugar Glider is a marsupial mammal and give birth to their young very early and provide most of their nourishment in their pouch as their baby develops. Northern Flying Squirrels are placental mammals that spend a much greater deal of time developing in their mother's body being nourished by their mother's placenta. If we go far back enough, we will see that these two animal so in fact share a rat like common ancestor which is the Mammalia.      

               

Week 2: Protein Synthesis

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Historical Influences On Charles Darwin

      Thomas Malthus was a social economist whose assertions of the population was the spark that ignited Darwin's theory of natural selection.  Malthus believed that if people did not control the number of children they had it would eventually lead to the demise of mankind.
      When Darwin was coming back from his voyage trying to put together the origins of new species he had heard Malthus' explanation that if it weren't for disease and famine, increasingly crowded cities would face over population. This lead Darwin to ponder the struggle for survival in the wild. He came to the conclusion that in the wild and human population alike, animals breed beyond there means. With limited resources the strong would survive and the weak would cease to exist.
      Darwin concluded that some variations of species would be better equipped to thrive and produce offspring than others. Eventually that species will multiply and be the only variation which is ideally adapted to it's environment. This theory is now known as his theory of natural selection.
      Though Thomas Malthus did not formally make any scientific contributions, Darwin's theory of natural selection can be observed essentially from an economical and social standpoint through Malthus's observations. It is especially helpful in the explanation of Darwin's work since natural selection cannot be formally observed first hand
(http://www.pbs.org/wgbh/evolution/library/02/5/l_025_01.html)
     Malthus's work is an example of limited resources playing a main role in the theory of natural selection. With a limited number of resources whether from an economical standpoint or in the wild, only those best suited to access of those resources can survive.
      It is possible that Darwin could have eventually come up with his theory later on without the help of stumbling upon Malthus's work but he indeed helped Darwin solve a major issue that he was having with his hypothesis if evolving species.
      The attitude of the church definitely hindered Darwin from wanting to publish his theory of evolution because he knew that it went against everything that everyone knew to be true. he knew that his theory would challenge the Bible and from examples of other scientists before him like Nicolaus Copernicus and Galileo Galilei, he would face persecution. But unlike his predecessors, his theory has yet to be accepted by the church to be true.